Fast algorithms for handling diagonal constraints in timed automata

A popular method for solving reachability in timed automata proceeds by enumerating reachable sets of valuations represented as zones. A na\"ive enumeration of zones does not terminate. Various termination mechanisms have been studied over the years. Coming up with efficient termination mechanisms has been remarkably more challenging when the automaton has diagonal constraints in guards. In this paper, we propose a new termination mechanism for timed automata with diagonal constraints based on a new simulation relation between zones. Experiments with an implementation of this simulation show significant gains over existing methods.Comment: Shorter version of this article to appear in CAV 201

No Efficacy of the Combination of Lopinavir/Ritonavir Plus Hydroxychloroquine Versus Standard of Care in Patients Hospitalized With COVID-19: A Non-Randomized Comparison

Objectives: No specific treatment has been approved for COVID-19. Lopinavir/ritonavir (LPV/r) and hydroxychloroquine (HCQ) have been used with poor results, and a trial showed advantages of combined antiviral therapy vs. single antivirals. The aim of the study was to assess the effectiveness of the combination of antivirals (LPV/r and HCQ) or their single use in COVID-19 hospitalized patients vs. standard of care (SoC). Methods: Patients ≥18 years with SARS-CoV-2 infection, defined as positive RT-PCR from nasal/oropharyngeal (NP/OP) swab or positive serology, admitted at L. Spallanzani Institute (Italy) were included. Primary endpoint: time to invasive ventilation/death. Secondary endpoint: time to two consecutive negative SARS-CoV-2 PCRs in NP/OP swabs. In order to control for measured confounders, a marginal Cox regression model with inverse probability weights was used. Results: A total of 590 patients were included in the analysis: 36.3% female, 64 years (IQR 51-76), and 91% with pneumonia. Cumulative probability of invasive ventilation/death at 14 days was 21.2% (95% CI 17.6, 24.7), without difference between SOC, LPV/r, hydroxychloroquine, HCQ + LPV/r, and SoC. The risk of invasive ventilation/death in the groups appeared to vary by baseline ratio of arterial oxygen partial pressure to fractional inspired oxygen (PaO2/FiO2). Overall cumulative probability of confirmed negative nasopharyngeal swabs at 14 days was 44.4% (95% CI 38.9, 49.9), without difference between groups. Conclusion: In this retrospective analysis, we found no difference in the rate of invasive ventilation/death or viral shedding by different strategies, as in randomized trials performed to date. Moreover, even the combination HCQ + LPV/r did not show advantages vs. SoC

Wireless coils based on resonant and nonresonant coupled-wire structure for small animal multinuclear imaging

Earlier work on RF metasurfaces for preclinical MRI has targeted applications such as whole‐body imaging and dual‐frequency coils. In these studies, a nonresonant loop was used to induce currents into a metasurface that was operated as a passive inductively powered resonator. However, as we show in this study, the strategy of using a resonant metasurface reduces the impact of the loop on the global performance of the assembled coil. To mitigate this deficiency, we developed a new approach that relies on the combination of a commercial surface coil and a coupled‐wire structure operated away from its resonance. This strategy enables the extension of the sensitive volume of the surface coil while maintaining its local high sensitivity without any hardware modification. A wireless coil based on a two parallel coupled‐wire structure was designed and electromagnetic field simulations were carried out with different levels of matching and coupling between both components of the coil. For experimental characterization, a prototype was built and tested at two frequencies, 300 MHz for 1H and 282.6 MHz for 19F at 7 T. Phantom and in vivo MRI experiments were conducted in different configurations to study signal and noise figures of the structure. The results showed that the proposed strategy improves the overall sensitive volume while simultaneously maintaining a high signal‐to‐noise ratio (SNR). Metasurfaces based on coupled wires are therefore shown here as promising and versatile elements in the MRI RF chain, as they allow customized adjustment of the sensitive volume as a function of SNR yield. In addition, they can be easily adapted to different Larmor frequencies without loss of performance

Volume coil based on hybridized resonators for magnetic resonance imaging

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Extending a Birdcage Coil for Magnetic Resonance Imaging of a Human Head with an Artificial Magnetic Shield

In magnetic resonance imaging, a birdcage coil is the most commonly used volumetric resonator creating a highly homogeneous radiofrequency magnetic field in a conductive sample. An artificial magnetic radiofrequency shield was recently shown to improve the magnetic field amplitude per unit power (transmit efficiency) of a preclinical birdcage coil by reducing the intrinsic losses in the coil and increasing power absorbed by the sample. In this paper, we propose a new application of an artificial shield in clinical MRI. Thanks to the proposed artificial shield a birdcage coil for human brain imaging operating at 300 MHz (Larmor frequency of protons at static fields of 7 T) can be expanded to increase free space. As a result, the coil becomes more comfortable for the patient and keeping comparable transmit efficiency. The same extended coil with a conventional copper shield would have at least 10% lower efficiency. The proposed artificial shield is implemented as an annular-ring cavity-backed slot in a copper cylinder that tightly surrounds the birdcage. To demonstrate the effect, radiofrequency magnetic field and specific absorption rate distributions were compared numerically and experimentally for the initial and extended coils with different shields.Peer reviewe

Measurement and simulation of the polarization-dependent Purcell factor in a microwave fishnet metamaterial

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Complete Electromagnetic Dyadic Green Function Characterization in a Complex Environment—Resonant Dipole-Dipole Interaction and Cooperative Effects

International audienceThe Green function completely encapsulates a system's linear response to external sources, and plays a central role in optics, electromagnetism, and acoustics. In electromagnetism, a broad range of phenomena are connected to the Green function, including the local density of optical states, superradiance, and the cooperative Lamb shift. Therefore, knowing the Green function is important for progress in fields as diverse as cavity quantum electrodynamics, plasmonics, metamaterials, and photovoltaics. However, experimentally characterizing the full complex Green function is challenging, as it requires amplitude and phase sensitive measurements with deep-subwavelength spatial resolution. Here, we report a method to characterize the full complex Green function with a resolution of λ=100 by measuring the mutual impedance between two dipoles at microwave frequencies. We apply it to a resonant planar cavity, with both parallel and nonparallel sides, and also explore the effects of modal resonances in a dielectric cube on dipole-dipole interactions. The ability to characterize the Green function with high spatial resolution provides a unique way to investigate cooperative effects in complex photonic systems

Prognostic factor analysis and long-term results of the TAX 323 (EORTC 24971) study in unresectable head and neck cancer patients.

In the TAX 323 (EORTC 24971) phase III trial enrolling patients with unresectable locoregionally advanced squamous cell carcinoma of the head and neck (LA-SCCHN), the addition of docetaxel (T) to cisplatin and 5-fluorouracil (PF)-based induction chemotherapy prior to definite radiotherapy significantly improved progression-free survival (PFS) and overall survival (OS). The data were updated for PFS, OS and treatment-related long-term side-effects. Baseline clinical and laboratory data of 17 variables were collected and subjected to univariate and multivariate prognostic factor analyses for OS. All 358 patients randomised between 1999 and 2002 were included in the long-term analysis with a median follow-up of 8.6 years. The primary end-point of PFS remained significantly improved with TPF compared with PF (adjusted hazard ratio [HR], 0.70; 95% CI, 0.56-0.88, p = 0.002), translating into a persisting benefit in OS (adjusted HR, 0.75; 95% CI, 0.60-0.95, p = 0.015). Long-term side-effects in the TPF/PF arms comprised tracheostomy (7%/5%), feeding tube dependency (3%/6%) and gastrostomy (11%/11%). Second malignancy occurred in 8%/3%, respectively. Out of 177 patients randomised to the TPF arm, 160 were included in the multivariate analysis. Grade 2 or more dysphagia (p = 0.002) and grade 2 or more pain (p = 0.004) at baseline were identified as independent negative prognostic factors. In addition, OS differed across primary tumour sites (p = 0.027) and was worse in patients with a higher N-stage (p = 0.025). In LA-SCCHN patients treated with sequential chemoradiotherapy, TPF induction chemotherapy demonstrated long-lasting efficacy, superior to the PF regimen. Higher-grade dysphagia and pain are unfavourable prognosticators

On the Selection of Relevant Hardware Events for Explaining Execution Time Behavior

International audienceEstimating safe upper bounds on task execution times is required in the design of predictable real-time systems. When multi-core, instruction pipeline, branch prediction, or cache memory are in place, due to the considerable complexity static timing analysis faces, measurement-based timing analysis (MBTA) is a more tractable option. MBTA estimates upper bounds on execution times using data measured under the execution of representative scenarios. In this context, it is paramount understanding not only how the task execution time is affected during its execution but also what kind of interference the task is sensitive to. Events such as cache misses or pipeline stalls, for example, may lead to large variability in task execution times. Based on the fact that current platforms offer Performance Monitoring Units (PMUs) capable of counting hardware-level event occurrences, in this paper, we focus on the problem of selecting the events that have the most impact on task execution with the goal of enriching the collected information to better support MBTA. Unfortunately, PMU usually have a limited number of monitoring registers, making them unable to monitor all events at once. Our approach describes how to carry out the events selection even under this limitation. Results from our experiments, considering 15 different programs running on a Raspberry Pi, indicate that five selected events can explain the execution behavior of the programs with reasonable accuracy

A practical realization of an artificial magnetic shield for preclinical birdcage RF coils

In the most of magnetic resonance imaging (MRI) systems, a conventional radiofrequency (RF) electric shield is typically placed around an RF volume coil to avoid the interaction with the other components of the system. Disadvantageously metal shields reduce the transmit efficiency of the RF coil as well as its receive sensitivity due to out-ofphase reflection of electromagnetic waves. In contrast, an ideal magnetic shield having high surface impedance provides in-phase reflection, which can be promising for improvement of RF coil's performance. In this work, we propose an artificial magnetic shield based on a cylindrical miniaturized corrugated structure to improve characteristics of a small-animal birdcage coil at 7T. The coil was simulated in the presence of the metal and ideal magnetic shield as well as the proposed structure. The results demonstrate enhancement of the coil's performance in the presence of the proposed shield, which is comparable with an ideal one.Peer reviewe